Effect of formoterol with or without budesonide in repeated low-dose allergen challenge.

The use of combination therapy in mild asthma is debated. The current authors evaluated the effects of formoterol alone and a formoterol/budesonide combination inhaler on asthma deterioration induced by repeated low-dose allergen exposure. In total, 15 subjects with intermittent allergic asthma inhaled low doses of allergen on seven consecutive weekdays in a three-period, crossover, double-blind, double-dummy comparison between formoterol 4.5 microg Turbuhaler, budesonide 160 microg/formoterol 4.5 microg Turbuhaler and placebo, each taken as two puffs 30 min after allergen dosing. The outcome variables were: provocative dose of methacholine causing a 20% fall in forced expiratory volume in one second (PD(20)), exhaled nitric oxide fraction (F(eNO)), sputum eosinophils and prostaglandin D(2), and diary card recordings of symptoms (on a scale of 0-10), short-acting beta(2)-agonist use and evening forced expiratory volume in one second (FEV(1)). With placebo treatment, allergen exposure caused significant increases in airway hyperresponsiveness (geometric mean (coefficient of variation) PD(20): 397 (98) microg before versus 168 (82) microg after), F(eNO) (mean+/-sd 46+/-31 ppb before versus 73+/-46 ppb after) and asthma symptom score (mean+/-sd 0.39+/-0.55 before versus 0.68+/-0.67 after). Budesonide/formoterol abolished these changes and significantly improved baseline FEV(1). Formoterol alone, while providing symptom relief, was no better than placebo in protecting against the allergen-induced increase in airway inflammation. Signs of deteriorating asthma, provoked by low-dose allergen, are prevented by short-term use of budesonide/formoterol but not by temporary use of formoterol alone.

Early rise in exhaled nitric oxide and mast cell activation in repeated low-dose allergen challenge.

Repeated low-dose allergen inhalation challenge mimics natural allergen exposure, providing a model for early mechanisms in the triggering of asthma. The current authors performed a controlled study to evaluate the time course of changes in exhaled nitric oxide fraction (F(e,NO)) and urinary biomarkers of airway inflammation. Eight subjects with mild allergic asthma completed two 7-day repeated low-dose challenge periods, with diluent and allergen, respectively. Subjects were symptom free at inclusion and were investigated when not exposed to specific allergen. Pulmonary function and symptoms were followed, and F(e,NO) and urinary mediators were correlated to changes in airway responsiveness to histamine and adenosine. Despite no change in pulmonary function (forced expiratory volume in one second mean+/-sem fall 0.3+/-0.7 versus 0.6+/-1.0%, for diluent and allergen, respectively) and no asthma symptoms, repeated allergen exposure, in contrast to diluent, caused significant increases in histamine responsiveness (2.3 doubling doses), an early and gradual increase in F(e,NO) (up to a doubling from baseline) and a small increase in the mast cell marker 9alpha11beta-prostaglandin F(2) after adenosine challenge. In conclusion, serial measurements of exhaled nitric oxide fraction have the potential to provide a very sensitive strategy for early detection of emerging airway inflammation and subsequent changes in airway hyperresponsiveness to histamine.

Exhaled carbon monoxide is not elevated in patients with asthma or cystic fibrosis.

Increased levels of exhaled carbon monoxide (fractional concentration of CO in expired gas (FE,CO)), measured with an electrochemical sensor, have been reported in patients with inflammatory airway disorders, such as asthma, rhinitis and cystic fibrosis. This study aimed to evaluate these findings by using a fast-response nondisperse infrared (NDIR) analyser, and to compare these measurements with the fractional concentration of nitric oxide in exhaled air (FE,NO). Thirty-two steroid-naïve asthmatics, 24 steroid-treated asthmatics (16 patients with allergic rhinitis, nine patients with cystic fibrosis), and 30 nonsmoking healthy controls were included. CO measurements with the NDIR analyser were performed simultaneously with nitric oxide (NO) analysis (chemiluminescence technique). After 15 s of breath-hold, single-breath exhalations over 10 s were performed at two flow rates and end-tidal plateau concentrations were registered. An electrochemical CO sensor was used independently with an exhalation to residual volume, after a 15 s breath-hold. None of the two CO analysers gave a significant increase in FE,CO in the groups of patients with inflammatory airway disorders compared to controls. FE,NO was significantly elevated in steroid-naïve asthmatics and subjects with allergic rhinitis, but not in steroid-treated asthmatics and subjects with cystic fibrosis. Reducing exhalation flow rate by 50% gave a two-fold increase in FE,NO, while FE,CO was unaffected. A significant increase was seen in FE.CO, but not in FE,NO, when comparing with and without a 10 s breath-hold. In conclusion, the fractional concentration of carbon monoxide in expired gas was not increased in any of the patient groups, while the fractional concentration of nitric oxide in expired gas was significantly elevated in patients with steroid-naïve asthma and allergic rhinitis. Moreover, carbon monoxide was unaffected by flow rate but increased with breath-hold, suggesting an origin in the alveoli rather than the conducting airways.

Conditions in blood sampling procedures that extend the ex vivo stability of eosinophil activity markers in peripheral blood from allergic patients and healthy controls.

BACKGROUND: Serum-ECP, EG2-epitope on intracellular ECP and surface expression of CD9 and CD11b in peripheral blood eosinophils (PBE) are considered to be markers that mirror clinical parameters in allergic inflammation. OBJECTIVE: The aim was to investigate the impact of the blood sampling procedure on PBE markers and to identify optimal conditions for extended pre-analysis storage. METHODS: Blood, from healthy individuals and patients with allergic rhinitis/asthma, was collected in tubes with EDTA, citrate, or without anti-coagulant. The expression of EG2-epitope, CD9, and CD11b were analyzed in eosinophils and neutrophils after 1, 5, and 24 hours of storage at +4 degrees C, according to the FOG-method and flow cytometry. In vitro stimulation with fMLP/PMA was used for metabolic activity analysis and CD11b mobilization. Following a 1-hour clotting period at +20 to 22 degrees C, samples were stored at +4 degrees C and serum-ECP levels were measured. RESULTS: The EG2-epitope, serum-ECP, and CD9 were stable in samples from both healthy controls and allergic patients at all storage conditions. The EG2-epitope, serum-ECP and PBE count were significantly increased in the patient group, whereas no differences were observed in the expression of CD9 or CD11b. Both granulocytes and monocytes retained their metabolic activity for 24 hours. Neutrophils in citrate-blood increased their ability to respond to fMLP, as compared with EDTA-blood. CONCLUSION: In vitro analysis of selected activity markers and functional tests could be performed on granulocytes from both healthy individuals and allergic patients after 24 hours storage at +4 degrees C. The anticoagulant citrate seems to be preferable to EDTA when monocytes or CD11b expression are analyzed.

Selective CD8+ T cells accumulate in the lungs of patients with allergic asthma after allergen bronchoprovocation.

Our objective was to study whether CD4+ or CD8+ T cells expressing particular T cell receptors (TCR) would accumulate in the lungs of patients with allergic asthma following allergen exposure. We thus analysed the TCR Valpha and Vbeta gene usage of CD4+ and CD8+ lung and peripheral blood lymphocytes (PBL) of eight patients with allergic asthma before and 4 days after inhalation challenge with the relevant allergen. Lung cells obtained by bronchoalveolar lavage (BAL) and paired PBL samples were analysed by flow cytometry using a panel of anti-TCR V-specific monoclonal antibodies that encompass = 50% of the T cell repertoire. Lung-limited T cell expansions were recorded in both the CD4+ and the CD8+ subsets. In BAL CD8+, out of a total of 126 analyses, the number of T cell expansions increased from two to 11 after challenge, some of them dramatic. In BAL CD4+ the frequency of expansions was moderately increased already before challenge, but remained unchanged. A few expansions that tended to persist were noted in PBL CD8+. When analysing the overall change in TCR V gene usage the largest changes were also recorded in the BAL CD8+ subset. Specific interactions between T cells and antigens may lead to an increased frequency of T cells using selected TCR V gene segments. In this study we demonstrate that following allergen bronchoprovocation in allergic asthmatic subjects, T cell expansions preferentially emerge in the lung CD8+ T cell subset.

No signs of activity markers in peripheral blood despite increased bronchial reactivity after repeated low-dose allergen exposure.

The allergen inhalation test can be used as an experimental model to study pathophysiological events in allergic asthma. Repeated low-dose inhalations of allergen induce increased bronchial hyperresponsiveness (BHR) and resemble natural allergen exposure. The objective of the present study was to investigate whether eosinophil recruitment and activation in peripheral blood, differences in expression of lymphocyte surface antigens and increased bronchial responsiveness to histamine occur during and after repeated low-dose bronchial allergen challenge. Fourteen atopic asthmatic patients were challenged in a randomized double-blind manner for 7 days with either allergen in very low doses or placebo. We measured the concentration of eosinophils, eosinophil cationic protein (ECP) and the expression of the EG2-epitope on intracellular ECP in eosinophils and the expression of lymphocyte surface antigen markers in peripheral blood. The challenge period started and ended with a histamine provocation. The repeated low-dose allergen exposure resulted in a significant increase in BHR. No changes were seen in the placebo group. Concerning the inflammatory parameters in peripheral blood, no significant changes were seen during or after the week of low-dose allergen inhalations. Our results show that very low, repeated doses of allergen induce increased airway reactivity despite lack of evident clinical symptoms or signs of activation of inflammatory cells in peripheral blood.

Increased allergen-specific Th2 responses in vitro in atopic subjects receiving subclinical allergen challenge.

The study aimed to determine whether inhalation of subclinical allergen doses-leads to a shift in the balance between T helper (Th) 1 and Th2 cells in asthmatic patients. Elevated IgE requires allergen-specific T cells producing cytokines such as interleukin (IL)-4 or IL-13. Interferon-gamma (IFN-gamma) produced by Th1 cells counteracts the effects of IL-4. In nature, allergic persons are often exposed to low levels of allergen, leading to hyperreactivity, but not to acute allergic reactions. In this study, nine allergic persons inhaled low doses of allergen or placebo in a double-blind manner over seven consecutive weekdays. During the study, the bronchial responsiveness to histamine challenge increased, but no subject exhibited asthmatic symptoms. Blood was drawn on days 0, 1, 4, and 9, and the number of IL-4- and IFN-gamma-producing cells was measured by enzyme-linked immunospot (ELISPOT) assay after in vitro stimulation with a low-dose phytohemagglutinin (PHA) mixed with the relevant allergen or with PHA alone. In three of the four subjects receiving allergen, the IL-4/IFN-gamma ratio increased during the time of the study. No increase was seen in the placebo group. No increase was seen in serum IgE levels in any of the groups. We conclude that a shift in the balance between Th1 and Th2 cells can be detected in subjects exposed to subclinical allergen doses.

Combined antagonism of leukotrienes and histamine produces predominant inhibition of allergen-induced early and late phase airway obstruction in asthmatics.

We defined the contribution of histamine and leukotrienes to allergen-induced airway obstruction in asthmatics; 12 subjects with allergic asthma underwent identical allergen bronchoprovocations on four occasions. At a control session, all subjects displayed early (EAR) and late asthmatic (LAR) reactions. The mean (+/- SE) drop in FEV1 during EAR (0-2 h) and LAR (2-12 h) was 29 +/- 2% and 28 +/- 4%, respectively. Thereafter, the influence of 1 wk randomized pretreatment with the leukotriene receptor antagonist zafirlukast (Accolate) (80 mg twice daily), the antihistamine loratadine (10 mg twice daily), and the combination of both antagonists was assessed. Expressed as AUC FEV1 in percent of the control reaction, zafirlukast reduced the response during EAR and LAR by 62 +/- 11% and 55 +/- 12%, respectively (p < 0.05 versus control). Loratadine inhibited EAR and LAR by 25 +/- 14% and 40 +/- 16%, respectively (p < 0.05 versus control). Zafirlukast was significantly more effective than loratadine during EAR but not during LAR. The combination of zafirlukast and loratadine reduced the AUC FEV1 during EAR and LAR further, by 75 +/- 8% and 74 +/- 14%, respectively (p < 0.05 versus control). The combination was significantly (p < 0.05) more effective than either drug alone during the LAR. The findings indicate that leukotrienes and histamine together mediate the major part of both the EAR and the LAR following exposure of asthmatics to allergen. Combination of leukotriene antagonism and antihistamines may represent a new strategy for treatment of airway obstruction in asthma.

Inhibition of allergen-induced airway obstruction and leukotriene generation in atopic asthmatic subjects by the leukotriene biosynthesis inhibitor BAYx 1005.

BACKGROUND: Leukotriene receptor antagonists significantly blunt allergen-induced bronchoconstriction in asthmatic subjects. Inhibitors of leukotriene synthesis should theoretically provide similar protection, but conflicting results have been obtained when synthesis inhibitors have been tested in allergen challenge. BAYx 1005, a new inhibitor of leukotriene synthesis, was therefore evaluated in an allergen bronchoprovocation study. METHODS: Ten men with mild allergic asthma and bronchial hyperresponsiveness to histamine were recruited. On two different occasions each subject inhaled a single dose of allergen, previously determined to cause at least a 20% fall in forced expiratory volume in one second (FEV1) four hours after ingestion of 750 mg BAYx 1005 or placebo in a double blind crossover design. Urinary excretion of leukotriene E4 was measured before and during the challenges. RESULTS: The mean (SE) maximal fall in FEV1 was 7.1 (1.7)% after BAYx 1005 and 21.0 (3.0)% after placebo (p < 0.001). The mean difference between treatments was 13.9 (95% CI 7.0 to 20.8) for the maximal fall in FEV1. All subjects were protected by BAYx 1005, the mean inhibition of the fall in FEV1 being 70.0 (7.0)%. The mean area under the curve (AUC) for urinary excretion of leukotriene E4 in the first two hours after the challenge was 1.7 (0.9) after placebo and 0.4 (0.6) after BAYx 1005 (difference = 1.3 (95% CI-0.1 to 2.7); p < 0.05). CONCLUSIONS: These results indicate that BAYx 1005 is a potent inhibitor of allergen-provoked leukotriene synthesis in asthmatic subjects and lend further support to the suggestion that leukotrienes are important mediators of allergen-induced bronchoconstriction.

Eosinophil activity markers in peripheral blood have high predictive value for bronchial hyperreactivity in patients with suspected mild asthma.

The present study aimed to evaluate the predictive value of eosinophils and markers of their activity for bronchial hyperreactivity (BHR) in a population of patients with recently developed clinical symptoms of asthma. The activation of eosinophils was estimated by measuring eosinophil cationic protein (ECP) in serum. In addition, flow cytometry was used to measure the expression of the EG2-epitope on intracellular ECP in eosinophils from peripheral blood. Twenty-eight consecutive patients with clinical history of asthma were studied. Of the 28 patients, 18 had a positive bronchial challenge test measured as PD20 < or = 1600 micrograms histamine. A significantly higher concentration of eosinophils and a trend to higher ECP in the peripheral blood was found in the hyperreactive group than in the nonreactive group. However, the intracellular expression of ECP did not correlate with the PD20 value, and no significant difference between the groups was found. With one eosinophil activity marker, either serum ECP or EG2, BHR could be predicted in 70% of the patients. If we combined any two of the activity markers (serum ECP, EG2, or the percentage of eosinophils), the predictive value increased to 100%. We conclude that the blood eosinophil concentration, as well as, to some extent, serum ECP, has a high specificity for BHR in patients with recently developed clinical symptoms of asthma. Despite normal bronchial reactivity, some patients had signs of activated eosinophils, i.e., high serum ECP and increased EG2 expression. Thus, these markers may reflect early stages in the development of BHR. Our results also indicate that a combined evaluation of percentage of eosinophils and of eosinophil activity markers is of clinical value to predict BHR.

Allergen-induced inflammation in the nose: a comparison of acute and repeated low-dose allergen exposure.

To investigate allergic rhinitis induced by two experimental provocation models, we compared local inflammation with markers of eosinophil activity in peripheral blood. Patients with strictly seasonal allergic rhinitis were selected and investigated outside the pollen season. An acute challenge with increasing doses of allergen every 15 min until symptoms occurred was performed in nine patients. Nasal lavage and blood samples were taken before and 4 and 24 h after challenge. After a 6-week washout period, 10 patients were submitted to 7 days of repeated low allergen exposures. One small dose (approximately equal to 1/100 of the acute dose) was given each day. Blood and lavage samples were taken prior to and after the period. As control four patients were challenged with diluent only. The acute challenge resulted in sneezing and nasal discharge and blockage and was accompanied by a rise in histamine and eosinophil cationic protein (ECP) in lavage fluid after 4 h and continuing after 24 h, when there also was a rise in the number of eosinophils and ECP in peripheral blood. The repeated low-dose exposures caused very few symptoms but produced increased ECP in the lavage fluid and a trend toward increased histamine concentration. There were no changes in ECP, intracellular EG2 binding, or number of eosinophils in the blood. No changes were seen in the control group. Our findings show that changes in eosinophil mediator release in nasal lavage can be seen after very low, but repeated, allergen exposures despite no, or minimal, clinical symptoms.

Spirometry and ventilation-perfusion inequality in patients with mild allergic asthma before and during the pollen season.

Several studies on asthma have shown a low correlation between gas exchange and spirometry, especially after treatment with bronchodilators. The aim of the present study was therefore to examine both spirometry results and gas exchange during a pollen-free period and at the end of the pollen season in patients with mild and well-controlled allergic asthma. Pulmonary gas exchange was studied using a modified form of the multiple inert gas elimination technique. Lung volumes and forced expiratory flows were measured by common spirometry. During the non-pollen season, spirometry and forced expiratory flows were within the reference values in all but one patient, who had decreased indices for airway flow. Three other patients showed signs of minor gas exchange impairment. During the pollen season, FRC was slightly increased (P < 0.05) and MEF50 was slightly decreased (P < 0.05) for the group. Two patients had an increased index for gas exchange impairment (log SDQ was 0.64 and 0.59) and four patients had borderline log SDQ (0.50 to 0.56). However, the mean log SDQ was not increased in the pollen season. The results show that, both in the pollen season and in the pollen-free season, low degrees of gas exchange impairment could be present in pollen allergic asthmatic patients despite normal spirometry. The low degree of gas exchange impairment in some patients indicates the presence of airway inflammation with oedema and/or secretion. However, high degrees of ventilation-perfusion inequality were not observed in these patients where air flow rates were mainly normal.

Anaphylactic reactions to sunflower seed.

We report on four patients sensitized to sunflower seed. Three of them developed anaphylaxis and one chronic bronchial asthma. All four patients reacted the first time sunflower seeds were ingested, and all had kept cage birds fed on sunflower seeds. Therefore, the route of sensitization was probably by inhalation of airborne sunflower seed allergens. Investigation of this type of hypersensitivity in 84 atopic patients showed that only three patients were RAST-positive, indicating that this allergy is fairly uncommon. On the other hand, when atopic persons are exposed to cage birds, the rate of sensitization is rather high, as indicated by the fact that in this category 79% were skin prick positive and 21% were unequivocably RAST positive to sunflower seed.

Single-breath nitric oxide measurements in asthmatic patients and smokers.

Exhaled nitric oxide (NO) concentrations were measured in asthmatic outpatients and in non-smoking and smoking healthy controls. In single exhalations, NO showed a peak suggestive of airway origin in both controls and asthmatic patients. The peak NO concentration was higher in asthmatic patients and lower in smokers than in non-smoking controls (p < 0.05). The findings support a role for NO in the host defence response in asthma and suggest that NO measurements can discriminate between different types of lung disorders.

Increase in non-specific bronchial responsiveness after repeated inhalation of low doses of allergen.

The development of bronchial hyperresponsiveness (BHR) in asthma is considered to be caused by inflammation of the airway. In IgE-mediated allergy BHR is related to the occurrence of late phase reactions. We have previously shown that exposure to low doses of allergen can cause isolated late reactions. These findings are potentially of clinical importance, since exposure to low, subclinical allergen doses may lead to bronchial inflammation and increasing bronchial responsiveness without necessarily causing immediate bronchoconstriction. This study was performed to investigate whether repeated exposure to low doses of allergen could induce a change in BHR. The trial comprised two groups of five and eight patients with a history of allergic asthma. They were submitted to a series of allergen inhalations for 5-7 days. They were given the same low allergen dose (1-10 biological units) each day. Before and after the allergen exposure period histamine challenges were performed. After the week of allergen inhalation the bronchial responsiveness was increased in 11 of 13 patients.

Pulmonary gas exchange response following allergen challenge in patients with allergic asthma.

Pulmonary gas exchange was studied in 8 patients with allergic asthma before and after allergen challenge. Ventilation-perfusion relationships were assessed by the multiple inert gas elimination technique and forced expiratory flow by conventional spirometry. Measurements were made before, 7-8 minutes, and 0.5, 2.5 and 5 hours after challenge. During baseline conditions all patients showed normal forced expiratory flow (FEV1 3.9 +/- 0.77 (SD) l) and gas exchange expressed as the dispersion of pulmonary blood flow, log SDQ (0.35 +/- 0.08), (one of the common descriptors of ventilation-perfusion (VA/Q) inequality). Immediately after challenge there were significant decreases in FEV1 (to 2.3 +/- 0.75 l) and arterial PO2 (from 13.1 +/- 0.9 to 9.5 +/- 1.2 kPa). The developed ventilation-perfusion inequalities were similar to those found in other asthma studies, i.e. mainly a broad (log SDQ increased to 0.73 +/- 0.30) and sometimes bimodal distribution of the perfusion. Thirty minutes after challenge FEV1 significantly improved to 3.2 +/- 1.18 l while log SDQ remained high (0.71 +/- 0.32). Two and a half hours after challenge log SDQ was reduced and almost normalized to 0.38 +/- 0.07. Five patients developed a late phase reaction with decreasing flow rates after 5 hours. Three of these patients also showed increased log SDQ. There was no clear relationship between gas exchange mismatch and reduced forced expiratory flow. The results support the hypothesis that reduced expiratory flow and gas exchange impairment are caused by different pathophysiological mechanisms.

Airways responses to ipratropium bromide do not vary with time in asthmatic subjects. Studies of interindividual and intraindividual variation of bronchodilatation and protection against histamine-induced bronchoconstriction.

Bronchial histamine provocation tests were performed in nine patients with nonallergic asthma on four consecutive days 45 minutes after inhalation of placebo or ipratropium bromide in a dose-response manner (40 micrograms, 200 micrograms, and 800 micrograms). The drugs were administered double-blind, one dose on each day. This procedure was repeated identically after three to nine months to investigate whether the bronchial responses to ipratropium bromide are constant or change with time. Ipratropium bromide induced a significantly better bronchodilation and protection against histamine-induced bronchoconstriction than placebo with no differences between the three doses. No correlation between bronchodilatation and protection was found. In six asthmatic patients ("responders") ipratropium bromide induced a significant protective effect against histamine-induced bronchoconstriction but no dose-response relationship was found. In three patients none or a very poor protective effect was found at all dose levels ("nonresponders"). The protective effect of ipratropium bromide against histamine-induced bronchoconstriction did not differ between the first and second occasion. Thus, the bronchoprotection differed between different asthmatic subjects but did not vary with time (three to nine months) within the same subject. This finding seems to be of clinical importance since it implicates that the effect of anticholinergic agents on the airways is predictable.

Late asthmatic reactions and bronchial variability after challenge with low doses of allergen.

Late allergic inflammatory reactions are probably of major importance for the development of asthma. In order to study the occurrence of early and late asthmatic reactions after challenge with different doses of allergen, inhalation provocation tests were performed in 13 patients with mild or moderate symptoms of allergic asthma. The provocation series was started with a low allergen dose (0.1-10 BU), which was then increased in successive ten-fold increments at intervals of 1 week until a pronounced bronchial reaction developed. Three different reaction patterns were observed. Six patients showed an isolated late reaction to relatively low doses of allergen. In four patients an immediate reaction was followed by a late reaction--a so-called dual response, and in three patients only an immediate reaction occurred. In four of the six patients who showed only a late reaction a higher allergen dose was given and this resulted in dual reactions in all four. One patient was challenged with an even higher dose, to which she reacted with an immediate response alone. After a late reaction, bronchial variability with low PEF values was observed over a period of several days. It is thus possible for an isolated late asthmatic reaction to be provoked by a low dose of inhaled allergen. This can be of clinical importance, repeated small doses of allergen may be unnoticed but still give bronchial inflammation and asthmatic symptoms.

Bronchial provocation studies in farmers with positive RAST to the storage mite Lepidoglyphus destructor.

Bronchial provocation studies with L. destructor (L. des.) extract were made on 12 farmers with asthma who were exposed daily to stored hay and grain and had positive radio-allergo-sorbent test (RAST) to L. des. All 12 farmers developed more than a 20% fall in FEV1 to the extract. None of the symptomatic farmers who were also RAST positive to the L. des. culture medium developed an asthmatic reaction to the medium extract. Neither four healthy farmers nor two patients with asthma caused by D. pteronyssinus (D. pt.) responded to L. des. or the L. des. culture medium. Challenges with D. pt. extract were negative in two symptomatic farmers who were RAST positive to L. des. and negative to D. pt. The present study further supports our previous hypothesis that there is an IgE-mediated immunological mechanism behind L. des.-induced asthma in farmers and that atopic farmers are liable to develop occupational asthma caused by allergy to L. des..